This study will investigate the physiological properties of descending inputs to a primary sensory neuropil and the plasticity within this structure that highlights behaviorally significant sensory inputs. The proposed research will be performed in the electrosensory lateral line lobe (ELL) of mormyrid electric fish, a cerebellum-like structure in the medulla. The ELL acts as an adaptive filter in which predictable electrosensory inputs, such as those which are self-generated, are removed from the electrosensory processing stream. The probable mechanism is that of plasticity in the effects of predictive signals conveyed by parallel fibers. Specific Aim 1 will determine the activity of ELL parallel fibers by recording from the granule cells that give rise to them. Responsiveness of these cells to naturally occurring predictive signals, such as motor commands and proprioceptive signals, will be tested. Specific Aim 2 will examine the responses of ELL cells to these naturally-occurring predictive signals conveyed by parallel fibers, with a focus on plastic change following a period of association with peripheral electrosensory stimuli. The results of the project will be relevant to the general issues of descending control of sensory processing, storage of sensory information, and cerebellar function.